Update to null safety

Update the code to use null safety and upgrade the flutter version

Merge in the pull request with the build error

Fix up the error from the pull request

Update IOS

Update IOS to match the android changes.

Fix up IOS to correctly handle recording/streaming independently.
Add in adaptive bit rate to IOS
Add in the stats callback (although less data to return)

Fix OpenGL

• Streams correctly in all directions now with openGL. Defaults to openGL being on
  in the example app
• Changed the way the preview is displayed to do a boxrotation on the preview widget.
  Still a race condition here that means sometimes it doesn't update correctly.

Fix android's use of the camera2 api

• BREAKING CHANGE: moved the useOpenGL call to the initialiation
  of the sytem and not to each call.
• Allow the recording/streaming to work independently on
  android.
• Change how the recroding/streaming happens to avoid issues with
  the camera2 api.

Fix android restart

• Fix restarting on android. Can stop and restart now and it all works.

Fix streaming on android

0.2.2

Update to 0.2.2

Fix issues with Android

• Add in github workflows to test/publish the package
• Copy the video encoder from the pedro library and update
  to make it not message with sizes for the surface, but
  include the rotation to make rotation work without opengl.
• Fix up issues with stopping on Android.

Using openGL for better rendering

• Fixed up issues with the stopVideoStreaming api.
• Added a flag to use an openGL surface on android to allow for
  correct rotation when encoding, also sets up to do filters.

Android fixed and working

Android correctly sending video to the rtmp servers.